1. Field of the Invention
The present invention relates to vehicle exhaust systems. More particularly, the present invention relates to an exhaust control apparatus for use on a motorcycle, in which the apparatus is operable to ensure a smooth flow of an exhaust gas.
2. Description of the Background Art
Exhaust systems are conventionally used with virtually all types of vehicles, to dampen and muffle sound made by the engine. A number of flow control valves are known for controlling exhaust flow through an exhaust pipe.
One example of a known motorcycle exhaust control apparatus which mounts a valve in an exhaust passage of an engine exhaust system, and uses the valve to control a flow rate of exhaust gas in the exhaust passage, is disclosed in Japanese Unexamined Patent Publication Hei7 (1995)-145732. The motorcycle exhaust control apparatus described in this reference is somewhat effective, provided that the valve is mounted on the exhaust pipe which constitutes an exhaust passage, and the valve can be opened or closed. FIG. 18 of the accompanying drawings is a reproduction of FIG. 2 in Japanese Unexamined Patent Publication Hei7 (1995)-145732, wherein the reference numbers from the original publication are maintained.
As shown in FIG. 18, the motorcycle exhaust control apparatus described in Japanese Unexamined Patent Publication Hei7 (1995)-145732 includes an exhaust valve 20, which allows a shaft 22 to penetrate a cylindrical surface of an exhaust pipe 21. The exhaust valve 20 includes a throttle plate 23 attached to the shaft 22 for controlling an exhaust flow rate. The shaft 22 penetrates the approximate center of the pipe 21, extending along a line corresponding to the diameter of the pipe 21.
However, in the motorcycle exhaust control apparatus described in Japanese Unexamined Patent Publication Hei7 (1995)-145732, since the shaft 22, extends across the pipe 21 at the approximate center of the pipe 21, exhaust gas which flows through the approximate center of the pipe 21 is forced to flow in a roundabout route around the shaft 22. Hence, a turbulent flow is generated inside of the pipe 21, with the result that that the exhaust efficiency is lowered.
Therefore, a need still exists for an exhaust control apparatus for a motorcycle which can ensure a smooth flow of an exhaust gas when an exhaust valve 20 is arranged in an exhaust passage including an exhaust pipe.